System for providing signals from an auxiliary audio source to a radio receiver using a wireless link

ABSTRACT

An apparatus and method are provided for transmitting audio signals from an auxiliary source such as a satellite broadcast receiver or a CD or cassette player to a radio receiver located, for example, in a vehicle, using a wireless link. The apparatus comprises a scanning device for locating open radio frequencies in the RF spectrum of the radio receiver. The apparatus displays plural RF channel options on a display device and provides a selection device with which a user selects an RF channel. The apparatus modulates the audio signals using the selected radio frequency, and the user tunes the vehicle radio receiver to the selected RF channel. The scanning device continuously scans for open RF channels and monitors the quality of the RF channel already selected for use as the wireless link. The apparatus provides the user with an indication to select another open channel when the RF channel in use degrades.

FIELD OF THE INVENTION

The invention relates to a system for providing audio signals from anauxiliary source to a radio receiver, particularly a vehicle radioreceiver, using a wireless link. The invention further relates to amethod of providing audio signals to a radio receiver by automaticallyselecting a number of low noise radio frequencies for wireless signaltransmission from the auxiliary source to the radio receiver andproviding user controls to select one of the frequencies fortransmission.

BACKGROUND OF THE INVENTION

A number of systems exist which use an existing audio system in avehicle for playback of audio signals from a compact disc (CD) player,tape cassette player, satellite broadcast receiver, or other auxiliaryaudio source. These existing systems are designed to play back thesignals from the auxiliary audio source using a number of differentmethods. For example, one system receives satellite broadcast signalsand provides them to the optical head of a CD player, or the magnetichead of a tape cassette player, already installed in the vehicle. Thissystem is disadvantageous because it requires the user to install aremovable adapter to couple the satellite broadcast signal to theoptical or magnetic head of the vehicle audio system.

In other systems, signals from an auxiliary audio source such as a CD orcassette player are coupled to a vehicle radio receiver via a wirelesslink such as an FM wireless link. In one system, for example, signalsfrom the auxiliary audio source are frequency translated to the FMfrequency band and are then broadcast from a transmitter in the vehicleon several fixed frequencies for reception by the vehicle radioreceiver. A user then selects one of these frequencies on the vehicleradio receiver to listen to the transmitted signals. In another system,a user first selects a radio frequency in the FM band that is not beingutilized in the local area, and then tunes the existing vehicle radioreceiver to the selected frequency. The user then tunes a transmitter inthe vehicle to the same frequency. The transmitter receives a signalfrom a CD player and transmits the signal at the selected frequency.

The two types of wireless FM systems described above are disadvantageousbecause they do not provide for automatic monitoring of the radiofrequencies used for retransmitting signals from the auxiliary audiosource via the wireless link to the existing vehicle radio receiver. Theradio frequencies selected by the user, or the fixed frequencies used bythe transmitter, may be subject to interference and poor signal quality.In addition, the manual selection of a suitable radio transmissionfrequency is inconvenient to users.

A need therefore exists for an audio coupling system that overcomes theaforementioned drawbacks of the existing systems. Specifically, a needexists for a radio frequency or RF-coupled satellite broadcast receiverfor vehicles which provides a wireless link to an existing vehicle radioreceiver. In addition, a need exists for an RF-coupled satellitebroadcast receiver for vehicles which automatically selects optimalradio frequencies for wireless transmission to the vehicle radioreceiver.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, an RF-coupledsatellite broadcast receiver is provided which scans a radio frequency(RF) band in which a radio receiver, preferably but not necessarily in avehicle, can be tuned for signal reception. The RF-coupled satellitebroadcast receiver selects at least one open RF channel having thelowest noise floor for retransmission of the received satellitebroadcast signal to the radio receiver.

In accordance with another aspect of the present invention, theRF-coupled satellite broadcast receiver selects a plurality of open RFchannels having low noise floors and is capable of retransmitting thereceived satellite broadcast signal on any of these available RFchannels. The available RF channel information is provided to the user.The user selects one of these channels and then tunes the vehicle radioreceiver to the selected channel to listen to the satellite broadcastprogram.

BRIEF DESCRIPTION OF DRAWINGS

The various aspects, advantages and novel features of the presentinvention will be more readily comprehended from the following detaileddescription when read in conjunction with the appended drawings, inwhich:

FIG. 1 is a block diagram of an auxiliary audio system constructed inaccordance with an embodiment of the present invention to provide audiosignals to an existing radio via a wireless link;

FIG. 2 illustrates the installation of the system depicted in FIG. 1 ina vehicle in accordance with an embodiment of the present invention;

FIG. 3 is a block diagram of an interface circuit constructed inaccordance with an embodiment of the present invention;

FIG. 4 is a flowchart depicting a sequence of operations forimplementing the system in FIG. 1 in accordance with an embodiment ofthe present invention;

FIG. 5 is a block diagram of a satellite broadcast receiver for use withthe system depicted in FIG. 1 in accordance with an embodiment of thepresent invention;

FIG. 6. is a block diagram of a level control and de-emphasis circuitfor use with the system depicted in FIG. 1 in accordance with anembodiment of the present invention;

FIG. 7 illustrates a scanning receiver constructed in accordance with anembodiment of the present invention; and

FIG. 8 illustrates an auxiliary audio signal processing and displaydevice constructed in accordance with an embodiment of the presentinvention.

Throughout the drawing figures, like reference numerals will beunderstood to refer to like parts and components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A system 10 for providing satellite broadcast signals 13 or audiosignals from another auxiliary audio source to an existing radioreceiver 24 (e.g., in a vehicle) using a wireless link 15 in accordancewith the present invention is depicted in FIG. 1. The system 10comprises an antenna 12 such as a satellite S-band antenna (operable atabout 2.3 Gigahertz) for receiving satellite broadcast signals. Theantenna 12 is connected via a coaxial cable 14, for example, to anauxiliary audio signal processing and display device 16, which ishereinafter referred to as the interface device 16. Another antenna 18is connected to the interface device 16 to transmit signals therefrom toa radio receiver 24 comprising a tuner 20 and an antenna 22.

The antenna 12 and its associated circuitry (e.g., a low noiseamplifier) can be connected internally or externally with respect to avehicle. The antenna 12 can be used to receive satellite digital audioradio service (SDARS), a satellite broadcast service recentlyestablished by the U.S. Federal Communications Commission (FCC), in avehicle. As shown in FIG. 2, the antenna 12 can be mounted on the roof17 or rear window 19 of a vehicle 23, for example. The cable 14 connectsthe antenna 12 to a remote unit 11 forming a part of the interface unit16 of FIG. 1. The remote unit 11 can comprise, for example, an SDARSreceiver. The remote unit 11 can be placed in the cab 25 of a car ortruck, for example. To avoid having to drill a hole in the truck or car23 to install the cable 14, a device 21 can be mounted on the exteriorof the vehicle's rear window 19 using an adhesive material whichsupports the antenna 12 and associated circuitry. The device 21 can becapacitvely coupled with another device 29 which is connected to thecable 14. The other device 29 can be mounted on the inside of the window19 opposite the first device 21 using the same adhesive material. Theremote unit 11 is connected to a display and control unit 27, alsoforming a part of the interface device 16 of FIGS. 1 and 8, via awireline 31 or wireless link to the dashboard or other location in viewof the driver. The display and control unit 27 can comprise the scanningreceiver, the RF modulation and transmission devices and the display andcontrol devices. In accordance with an embodiment of the presentinvention, the channels of the SDARS receiver can be changed remotelyusing the display and control unit 27. Alternatively, the interfacedevice 16 can be installed as a single unit on or near the dashboard andtherefore accessible to the driver of the vehicle 23. As described belowand illustrated in FIGS. 1 and 8, the interface device 16 (or, in thetwo-part installation shown in FIG. 2, the display and control unit 27)comprises a display 36 for indicating one or more RF channels to whichthe user can tune the radio receiver 24 to complete the wireless link15. The display and control unit 27 can also be provided with channelselection buttons 38, which are described below.

As shown in FIG. 1, the system 10 of the present invention comprises aDC power supply adapter 26 which can be inserted in the cigarettelighter socket 28 provided in the dashboard of most vehicles to providepower to the system 10. The interface unit 16 can also be configured asa portable device which can be disconnected from the vehicle andoperated from an AC outlet (using a suitable AC/DC converter) or frombatteries. Thus, the interface device 16 can be used inside a home, forexample, or in conjunction with a portable radio.

With continued reference to FIG. 1, the radio receiver 24 is preferablya conventional amplitude modulation (AM) and frequency modulation (FM)radio provided as standard equipment in many vehicles. The antenna 22 isconfigured to receive AM and/or FM signals. In accordance with thepresent invention, the radio receiver 24 need not be modified in any wayto output the audio programming provided by the satellite broadcastsignals or by another auxiliary audio source. The antenna 18 ispreferably an FM antenna, and the interface 16 device is operable toconvert the satellite broadcast signals received via the antenna 12 toFM-band signals for retransmission from the antenna 18 to the radioreceiver 24. Thus, the system 10 of the present invention operates withexisting radios. It is to be understood, however, that the presentinvention can be configured to operate with other types of receiversusing wireless links at radio frequencies other than the AM and FMbands.

The interface device 16 preferably comprises a display 36 for indicatingone or more radio frequencies that are selected by the interface devicefor providing the wireless link 15. In the example illustrated in FIGS.1 and 8, the interface device 16 has determined that the radiofrequencies of 88.5 Megahertz (MHz), 98.7 MHz and 103.5 MHz arerelatively low noise, open channels which can be used for the wirelesslink 15. The user can select one of these channels (e.g., 88.5 MHz) fortransmission by the interface device 16 by selecting one of thecorresponding buttons 30, 32 and 34 provided on the interface device 16.The buttons 30, 32 and 34 can be implemented as touch screen buttons,for example. The user then selects the same frequency (88.5 MHz in thepresent example) on the vehicle tuner 20 using a tuning dial 42 or oneof a number of preset buttons 35 provided on the radio receiver 24 forselecting a radio station. The selected radio channel (e.g., 88.5 MHz)is indicated on the tuner display 46 in a conventional manner. The tuner20 can also be a chassis with a tuner and a tape cassette player asindicated by the cassette slot 40. A CD player can be provided in lieuof, or in addition to, the cassette player. A volume control dial 44 isprovided in a conventional manner.

The interface device 16 will now be described in more detail withreference to FIG. 3. As shown in FIG. 3, the interface device 16includes an auxiliary audio source such as an S-band satellite receiver50. The satellite receiver 50 can also be operated in other RF bands andhave, for example, an L-band or UHF front-end for use with direct audiobroadcast (DAB) systems in different countries. The auxiliary audiosource can also be a CD or cassette player 52 or other device, and canbe located external to the interface device 16 via an external sourceinput if desired. The satellite receiver 50, described below inconnection with FIG. 5, preferably downconverts and processes thereceived satellite broadcast signal to obtain a baseband signal.Alternatively, the satellite receiver 50 can downconvert the satellitebroadcast signal to an intermediate frequency (IF). The output signalfrom the satellite receiver is processed via a level control andpre-emphasis circuit 54, which is described below in connection withFIG. 6. The level control and pre-emphasis circuit 54 provides acomposite stereo signal to an RF modulator 56.

In accordance with the present invention, the RF modulator 56 convertsthe composite signal to a radio frequency selected using a scanningreceiver 58. The scanning receiver 58 preferably continuously monitorsthe RF spectrum of the geographic area in which the vehicle is locatedvia an antenna 61 for open RF channels (i.e., RF channels that have notransmitted broadcast signals). The scanning receiver 58 also determineswhich of the open frequencies satisfy predetermined criteria for lownoise (e.g., comparatively small signal strength). In other words, thescanning receiver 58 locates RF channels having a signal-to-noise ratio(SNR) below a predetermined level (e.g., below about 5 decibels). TheseRF channels are generally not used by broadcast stations in a particulargeographic area and do not exhibit the hissing or muting oftenassociated with a weak broadcast signal that is unacceptable to alistener. When an RF channel is located which meets these criteria, thescanning receiver 58 provides the radio frequency to a microcontroller60. The microcontroller 60 is programmed to display at least one, andpreferably several, radio frequencies on the display 36 which representpossible low noise, open channels for the wireless link 15. Themicroprocessor 60 is also programmed to provide a user with a userinterface 66 with which to select one of the possible open channels(e.g., buttons 30, 32 and 34). For example, the microcontroller 60 canimplement the three buttons 30, 32 and 34 as a touch screen interface inconjunction with the display 36 for selecting any of three open channels(i.e., 88.5 MHz, 98.7 MHz or 103.5 MHz in the example shown in FIG. 1).Other aspects of the display 36 which represent advantages of asatellite receiver are described below with reference to FIG. 8.

After the user selects one of the channel options provided by thescanning receiver 58 for the wireless link 15, the microcontroller 60provides an output signal to the RF modulator to modulate the basebandor IF signal from the level control and pre-emphasis circuit 54 usingfrequency mixing. Accordingly, the audio signal from the auxiliary audiosource 50 or 52 is modulated onto the selected RF channel fortransmission via the wireless link 15, following amplification by an RFpower amplifier 64.

The starting point of the scanning receiver 58, that is, the first RFchannel of the algorithm controlling the scanning receiver 58, isselected automatically and randomly to avoid all receivers selecting thesame unused channels in a particular geographic area and to minimizevehicle-to-vehicle interference. It is to be understood that the RFchannel need not be in the FM radio broadcast spectrum. For example, thewireless link 15 can be implemented in the AM radio broadcast spectrum.In that case, the scanning receiver 58 and the RF modulator are operatedusing AM radio broadcast frequencies. The scanning receiver 58preferably commences scanning upon power-up of the interface device 16.The interface unit 16 also comprises a scan button 70, as shown in FIGS.1 and 8, which allows a user to manually initiate scanning via thescanning receiver 58.

An exemplary scanning receiver 58 is depicted in FIG. 7. The scanningreceiver 58 comprises an amplifier 72 to amplify the signals receivedvia the antenna 61. A scanning device 73 can be provided with an inputto receive signals from the microcontroller 60. When the scan button 70is activated by a user or the interface device 16 is turned on (i.e.,via button 41), the microcontroller 60 responds by sending a signal tothe scanning receiver 58 to initiate the scanning algorithm for thescanning device 73. The scanning device 73 is preferably programmed toscan every 200 kHz for operation in conjunction with an FM broadcasttransmission system in the United States. The scanning device 73 can beprogrammed to operate in accordance with different channel spacingallocations and radio frequency broadcast bands in other countries so asto scan every 100 kHz of the FM broadcast band in Europe, for example.The scanning device 73 is connected to a received signal strengthdetector 74 which provides a received signal strength indicator (RSSI)to the microcontroller 60. The microcontroller 60 determines if any ofthe scanned frequencies meet the pre-defined criteria for the wirelesslink is described previously. Weak channels are detected as low voltagesignals, whereas strong signals are detected at higher voltage signals.The microcontroller 60 preferably selects the three lowest energy orweak channels having the lowest voltages measured by the detector 74.Selected scanned frequencies which meet the pre-defined criteria areindicated on the display, as shown in FIGS. 1 and 8, by themicrocontroller 60.

As shown in FIG. 8, the display 36 can provide additional informationother than the radio frequencies of channels from which a user canselect for implementing the wireless link 15. The microcontroller canreceive data 43 from the satellite receiver relating to SDARS servicesvia an input line 75, as shown in FIG. 3. The SDARS services data 43 caninclude, for example, satellite broadcast channel number 45, artistname, audio program title and data channel information. The interfacedevice 16 also comprises the power button 41, the scan button 70, thesatellite broadcast channel selection buttons 38, as well as volumecontrol and tuning buttons 37 and 39. The microcontroller 60 canindicate via the display 36 the random channel selection of the scanningreceiver 58, the signal strength (i.e., RSSI) of satellite orterrestrially repeated SDARS signals, and visual effects (e.g., adynamic bar graph display corresponding to the output levels of theaudio program from the auxiliary audio source), among other displayableinformation. The display 36 can also indicate the user's currentfrequency selection 33 for the wireless link 15. In addition, selectedopen channels in metropolitan areas such as New York City or Los Angelescan be preset on the interface device 16 and selected via a button 47,for example.

The selection of an RF channel for the wireless link 15 will now bedescribed with reference to the flow chart depicted in FIG. 4. As statedpreviously, the scanning receiver 58 commences scanning an RF spectrum(e.g., the FM radio broadcast band) upon power-up or after the useractivates the scan button 70 on the interface device 16 (block 78). Thescanning receiver 58 preferably determines a number of RF channels(e.g., between one and three RF channels) to be open and to havesufficiently low noise for use as the wireless link 15 (block 80). If noRF channels can be located, the scanning receiver 58 continues to scan,as indicated by the positive branch of decision block 82. The scanningreceiver 58 preferably continuously scans even if suitable RF channelsare reported to the microcontroller 60 since conditions may change overtime. In accordance with another embodiment of the present invention,the scanning receiver 58 can interrupt scanning if a number of RFchannels are located which are suitable for the wireless link 15. Thescanning receiver 58 can then resume scanning after the scan button 70is activated or sound quality on the RF channel selected by the user forthe wireless link 15 decreases below a predetermined threshold. In themeantime, only the transmitting antenna 18 is operating, and thereceiving antenna 61 is not functional. In this case, the antenna 18 canserve as both a transmitting and receiving antenna with a splitterconnection to the RF power amplifier 64 and the scanning receiver 58,respectively, and the antenna 61 can be eliminated. In other words, theantenna 18 is connected to the scanning receiver 58 during the scanningmode and is disconnected from the RF amplifier 64. When a number of RFchannels have been located for the wireless link 15, the antenna 18 isused for transmitting on a selected one of the RF channels and scanningthrough the antenna 18 is interrupted.

With continued reference to FIG. 4, the microcontroller 60 displays thechannels selected by the scanning receiver 58 on the display 36 (block84). The user selects one of the channels indicated on the display 36and then tunes the radio receiver 24 to that channel (block 86). Theuser then commences monitoring the sound quality of the wireless link 15(block 88). As stated previously, the scanning receiver 58 preferablycontinuously scans. When the selected RF channel is determined by thescanning receiver to be above a predetermined noise threshold, thescanning receiver 58 provides a signal to the microcontroller 60 toindicate to the user via the display 36 and/or a sound generating devicethat sound quality is poor blocks 90 and 92). The user can then selectanother RF channel indicated on the display device 36.

An exemplary satellite receiver 30 is depicted in FIG. 5. The S-bandsignals received by the antenna 12 of FIGS. 1-3 are amplified byamplifier 96 prior to downconversion to an IF via a mixer 98 and a localoscillator (LO) 100. The recovered IF signal is then processed via an IFfilter and amplifier 102 prior to obtaining the digital basebandinformation transmitted via satellite. For example, the recovered IFsignal can be converted to a digital representation thereof using ananalog-to-digital converter (ADC) 104 prior to phase shift keying (PSK)demodulation by a demodulator 106 if the baseband signal isPSK-modulated at the broadcast station. The satellite broadcast signalscan be time division multiplexed (TDM) signals and may thereforecomprise information from a number of broadcast programs, as well ashaving TDM data representing the left and right stereo channelscorresponding to the same broadcast program. Accordingly, a TDMdemultiplexer 108 is provided in the satellite receiver 50 to recoverthe information from the TDM broadcast channels. The recoveredinformation corresponds to the satellite broadcast program selected bythe user via the user interface 66, for example, as indicated at 107.The recovered information can be processed at the broadcast stations toprovide forward error correction (FEC) coding, which is decoded using anFEC 110 decoder at the receiver 50. Finally, the recovered baseband datacan be converted into analog audio signals using an audio decoder 112such as an MPEG decoder.

In accordance with an aspect of the present invention, the interfacedevice 16 can be implemented to convert the radio receiver 24 into adual-mode receiver in a satellite broadcast system in which measuressuch as time and space diversity and terrestrial retransmission havebeen taken to improve satellite signal reception at the vehicle. Spaceand time diversity are useful when a mobile satellite receiver istraveling in a suburban or rural area where line of sight blockage withrespect to the antenna 12 and the satellite occurs due to bridges, treesand low buildings. On the other hand, terrestrial retransmission ofsatellite signals is useful in areas where tall buildings are located,such as central city and metropolitan areas.

In FM broadcasting, high audio frequencies are emphasized to improve thesignal-to-noise ratio (SNR). Thus, a conventional FM tuner such as thetuner 20 is provided with a de-emphasis circuit for obtaining a flatfrequency characteristic. Accordingly, the level of the output signalsfrom the satellite receiver 50 or the CD/cassette player 52 of FIG. 2are adjusted by the circuit 54 (shown in detail in FIG. 6) to preventthe attenuation of high audio frequencies by the de-emphasis circuit inthe tuner 20. Such processing is described in U.S. Pat. No. 5,448,757,issued to Hirata on Sep. 5, 1995, incorporated herein by reference. Withreference to FIG. 6, the left and right channels in the audio signalsrecovered by the satellite receiver are processed by a stereo modulator116 and an automatic level control (ALC) circuit 118 connected to theoutput of the pre-emphasis circuit 114. The stereo modulator 116modulates the audio signals from the satellite receiver 50 to acomposite signal. The ALC circuit 118 controls the input to the stereomodulator 116 to reduce distortion.

Although the present invention has been described with reference to apreferred embodiment thereof, it will be understood that the inventionis not limited to the details thereof. Various modifications andsubstitutions have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. All suchsubstitutions are intended to be embraced within the scope of theinvention as defined in the appended claims.

What is claimed is:
 1. A system for providing audio signals to a radioreceiver from an auxiliary audio source comprising: an input forreceiving said audio signals from said auxiliary audio source; aprocessing device connected to said input and operable to substantiallycontinuously monitor a selected radio frequency spectrum to identifyradio frequency channels that satisfy a predetermined open channelcriteria, and to automatically select at least one radio frequencysatisfying said predetermined open channel criteria at which to transmitsaid audio signals to said radio receiver via a wireless link, and tomodulate said audio signals on said selected radio frequency; and anantenna connected to said processing device and operable to transmitsaid audio signals to said radio receiver using said at least one radiofrequency; wherein said processing device further comprises an outputdevice for indicating said at least one radio frequency to a user toallow said user to tune said radio receiver to said at least one radiofrequency; and wherein said auxiliary audio source is a satellitebroadcast receiver and said output device also indicates at least one ofchannel identification data corresponding to a satellite broadcastsignal received via said satellite broadcast receiver, satellitebroadcast program data comprising at least one of an artist name, aprogram title, and ancillary data relating to said satellite broadcastprogram, output level data corresponding to said satellite broadcastreceiver, and received signal strength indicator data corresponding tosaid satellite broadcast signal.
 2. A system as claimed in claim 1,wherein said at least one radio frequency is selected from one of anamplitude modulation radio broadcast spectrum and a frequency modulationradio broadcast spectrum.
 3. A system as claimed in claim 1, whereinsaid processing device is operable to monitor the quality of said atleast one radio frequency, to select another radio frequency when saidat least one radio frequency degrades, and to generate a secondindication signal to instruct said user to tune said radio receiver tosaid another radio frequency.
 4. A system as claimed in claim 1, whereinsaid processing device is operable to randomly select a first radiofrequency which satisfies said predetermined open channel criteria fromsaid selected radio frequency spectrum in response to powering up ofsaid processing device.
 5. A system as claimed in claim 1, wherein saidprocessing device comprises a scanning receiver for automaticallyscanning said predetermined radio frequency spectrum and selecting aradio frequency therein for said wireless link.
 6. A system as claimedin claim 1, wherein said processing device is operable to automaticallyand dynamically identify a plurality of radio frequencies satisfyingsaid predetermined open channel criteria at which to transmit said audiosignals to said radio receiver.
 7. A system as claimed in claim 6,wherein said processing device is operable to display said plurality ofradio frequencies via said output device, and further comprises aselection device to allow a user to select one of said plurality ofradio frequencies, said processing device modulating said audio signalsusing the radio frequency selected via said selection device.
 8. Asystem as claimed in claim 7, wherein said processing device is operableto monitor the quality of the radio frequency selected via saidselection device, and to generate a signal to instruct said user toselect another of said plurality of radio frequencies when the radiofrequency selected via said selection device degrades.
 9. A system asclaimed in claim 1, wherein said radio receiver comprises a de-emphasiscircuit, said processing device comprising a pre-emphasis circuit forreducing the effect of said de-emphasis circuit on said audio signalstransmitted to said radio receiver.